1. Field of the Invention
The present invention relates generally to the field of magnetic resonance imaging (MRI) and pertains more specifically to an apparatus for and a method of single-sided MRI with a palm-sized probe.
2. Discussion of the Prior Art
Single-sided or remotely positionable MRI devices have many advantages which stem primarily from the fact they can produce images of in situ specimens without requiring that the device surround and confine the specimen being imaged. Fields of study include a wide range of heterogeneous specimens with diverse compositions such as polymers, epoxies, biological tissues, food products, construction materials, and porous media. By virtue of being single-sided, however, they also have unique characteristics which must be taken into consideration. For instance, a single-sided MRI device generates an inhomogeneous magnetic field. This fact, alone, has a very significant effect on how the device is designed and how it operates.
In order to obtain useable images of in situ tissue, for example, with a single-sided MRI device, there needs to be a defined measurement region within the inhomogeneous magnetic field which is specifically configured for nuclear magnetic resonance (NMR) imaging. More specifically, it is the measurement region which coincidently covers the tissue that is to be imaged during the operation of the MRI device. Although the specific configuration for the measurement region can be varied somewhat according to the desires of the operator, for medical and industrial applications the measurement region will typically have a nearly flat planar configuration. Further, the measurement region will typically be relatively thin.
As is well known to skilled artisans, MRI is a diagnostic apparatus that is extensively used in the medical field to non-invasively image internal biological tissue. As is also well known, MRI relies on the magnetic resonance of nuclei, and the fact that when nuclei are placed in the environment of a strong external magnetic field B0 they will each assume a discrete energy state. Further, NMR takes advantage of the fact that while nuclei are influenced by an external magnetic field, radio frequency (RF) energy will induce changes in their energy states to generate signals which are characteristic of the nuclear spin and its surroundings. The RF radiation which is most effective for inducing such changes has a particular frequency (known as the Larmor frequency) which depends on the magnitude of the magnetic field at the location of the nucleus.
One advantage of a small portable MRI system is that it provides a non-destructive mobile scanning tool that renders information in situ which would otherwise not be attainable. One disadvantage of the small portable models is that they conventionally provide a narrow field of view requiring frequent repositioning of the probe.
Ideally, a portable MRI system would have a lower cost and a higher productivity than conventional systems. With a system of this type, system performance can be enhanced. A primary purpose of the present invention is to solve this need and provide further, related advantages.
An apparatus for and a method of single-sided MRI with a palm-sized probe is disclosed. The probe includes a planar permanent magnet having a gap between the north and south poles of the magnet. Positioned in the gap are an RF coil and a pair of gradient coils. The gradient coils are located on either side of the RF coil. The probe further includes an RF tuning circuit and a gradient input. In use, the pair of gradient coils produce a controlled magnetic field gradient over the field of view thereby improving image resolution.